This invention relates generally to inkjet printers, and more particularly to unwanted ink aerosol emitted by such printers that can negatively affect image quality.
Inkjet printers have become increasingly inexpensive and increasingly popular. A typical inkjet printer usually has a number of common components, regardless of its brand, speed, and so on. There is a print head that contains a series of nozzles used to spray drops of ink onto paper. Ink cartridges, either integrated into the print head or separate therefrom, supply the ink. There may be separate black and color cartridges, color and black in a single cartridge, a cartridge for each ink color, or a combination of different colored inks in a given cartridge. A print head motor typically moves the print head assembly back and forth horizontally, or laterally, across the paper, where a belt or cable is used to attach the assembly to the motor. Other types of printer technologies use either a drum that spins the paper around, or mechanisms that move the paper rather than the print head. The result is the same, in that the print head is effectively swept across the paper linearly to deposit ink on the paper. Rollers pull paper from a tray, feeder, or the user""s manual input, and advance the paper to new vertical locations on the paper.
In general, there are two broad classes of inkjet printers: continuous-ink inkjet printers, and drop-on-demand inkjet printers. The earliest inkjet printers were continuous-ink printers. With this type of inkjet printer, a continuous stream of ink droplets is sprayed. Deflection plates are used to cause the ink to either reach the media, or drop in a return gutter. The inkjet nozzle typically uses a piezoelectric crystal to synchronize the droplets, and a charging tunnel selectively charges the drops that are deflected into the return gutter. Other droplets reach the media. Most inkjet printers today, however, use the drop-on-demand approach, which forces a drop of ink out of a chamber by heat or electricity. The thermal method is used by some manufacturers, in which a resistor is heated that forces a droplet of ink out of the nozzle by creating an air bubble in the ink chamber. By comparison, the electric approach employed by other manufacturers uses a piezoelectric element that charges crystals that expand and jet the ink onto the media.
A problem with at least some drop-on-demand inkjet printers is the presence of image-quality impairing aerosol. When a print head of the inkjet printer ejects the ink droplets from the nozzle, ideally they form a single drop that travels to the media. However, occasionally the emitting drops break up before they reach the media. These droplets are usually between two-to-three picaliters in size, as compared to the twelve picaliters in size of the desired, unbroken droplets. The smaller droplets stay suspended in air for a short duration of time, creating a mist or aerosol of ink between the media and the print head and/or the carriage assembly. This aerosol can cause image-quality defects and print artifacts on the media, and may cause the printer to malfunction. The result is a less-than-ideal printed image on the media, and potentially an improperly functioning printer. For these and other reasons, therefore, there is a need for the present invention.
The invention relates to using an electrostatic mechanism to improve image quality. A carriage assembly of the invention for such a printer includes one or more inkjet print heads, and an electrostatic mechanism. Each inkjet print head ejects ink from a corresponding ink supply in droplets as needed and aimed on a media. The droplets each have either an improper drop size or a proper drop size. The proper drop size is greater than a first threshold, whereas the improper drop size is less than a second threshold that is itself less than the first threshold. The electrostatic mechanism prevents droplets of the improper drop size from reaching the media. The mechanism has an electrostatic charge sufficiently great to affect the droplets having the improper drop size, without substantially affecting the droplets having the proper drop size.
An inkjet printer of the invention includes one or more ink supplies, one or more inkjet print heads, and an electrostatic mechanism. Each inkjet print head ejects ink from a corresponding ink supply or supplies as needed and aimed on a media. The ink is ejected in substantially properly sized droplets, while also at least occasionally ejected as an image quality-impairing aerosol. The electrostatic mechanism prevents the image quality-impairing aerosol from reaching the media without affecting the substantially properly sized droplets of ink.
A method of the invention includes ejecting substantially properly sized droplets of ink as aimed on a media. Concurrently, the method ejects undesired aerosol-sized droplets of ink substantially smaller than the substantially properly sized droplets of ink. The method electrostatically affects the undesired aerosol-sized droplets of ink to prevent them from reaching the media, while unaffecting the substantially properly sized droplets of ink.